The present invention relates generally to hydrotreating processing units and methods, and more particularly to a hydrotreating processing unit that includes a plurality of catalyst zones, where each catalyst zone includes at least one catalyst bed and further wherein the unit includes a vapor/liquid separation zone between the catalyst zones, where the vapor/liquid separation zone is associated with a stripping section for removing materials, such as hydrogen sulfide and ammonia, between the processing by one or more upper catalyst zones and further processing by one or more lower catalyst zones. The present invention also relates to hydrotreating methods with similar features.
Hydrotreating is a hydroprocessing process used to remove heteroatoms such as sulfur and nitrogen from hydrocarbon streams to meet fuel specifications and to saturate olefinic compounds. Hydrotreating can be performed at high or low pressures, but is typically operated at lower pressure than hydrocracking.
Hydroprocessing recovery units typically include a stripper for stripping hydroprocessed effluent with a stripping medium such as steam, or preferably hydrogen rich gas, to remove unwanted hydrogen sulfide. The stripped effluent is then heated in a fired heater to fractionation temperature before entering a product fractionation column to recover products such as naphtha, kerosene and diesel.
During the hydrotreating process, hydrogen is contacted with hydrocarbon in the presence of suitable catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen and metals from the hydrocarbon feedstock. In hydrotreating, hydrocarbons with double and triple bonds may be saturated. Aromatics may also be saturated. Some hydrotreating processes are specifically designed to saturate aromatics.
In hydrotreating units that are configured and arranged for processing feeds that include high nitrogen content (greater than 500 wtppm, or even greater than 1000 wtppm, and possibly up to 5000 wtppm) and high sulfur content (greater than 1 wt %, or even greater than 2 wt %, and possibly up to about 5.5 wt %), the catalyst volumes required are high because the ammonia and the hydrogen sulfide formed during the processing tend to inhibit the catalyst activity. In order to compensate for this, the volume of catalyst is increased and/or the unit is operated at a higher average bed temperature.
Accordingly, there is a need for methods and devices that enable hydrotreating of feeds with high nitrogen and sulfur content, but that allows for reduced volumes of catalyst and/or reduced average bed temperatures compared to current methods and devices.